Tiger nut (Cyperus esculentus var. sativa) as a
plant, its derivatives/uses and benefits are mainly discussed. The hunt for
lesser known and un-exploited crops, many of which are potentially valuable as
human and animal foods has been on the high side now to retain the equilibrium
between population growth and agricultural productivity, particularly in the
tropical and sub-tropical areas of the world. Tiger nut is an underutilized
crop of the family Cyperaceae, which produces rhizomes from the base and
tubers that are somewhat spherical. Pollination is by wind. Young tubers
are white, while older tubers are covered by a yellow outer membrane; they are
usually found within six inches of the ground surface. Vegetative colonies of
its plants are often produced from the tubers and their rhizomes. They are
usually preserved by sun drying for about three months before storage. It can be eaten raw, dried, roasted, or grated and can be
subjected to further processing. Its uses in cooking and as fuel, baking flour,
fish baits; milk in lieu of cows milk are outlined. Regarding the plant high
percentage of carbohydrates (mono- and di-), fibre, and oil (especially oleic
acid) and its moderately high level of protein, minerals (calcium, magnesium,
iron and phosphorous), and vitamins C and E makes it a good source of food for
humans and animals. It is a cheap source of nutrition for both the rich and the
poor. The health benefits reflect reduction of low density lipoprotein-cholesterol,
which is good for sports men and women and those intending to lose weight; it
is also said to serve as a cure for flatulence and diarrhea, and as control
against heart attacks, thrombosis and colon cancer, among others. The presence
of anti-nutrients like polyphenols and tannins can be eliminated by boiling in
water. The tiger nut, though under-utilized, is still a good food snack for all.
There is a need for awareness creation on tiger nuts inherent nutritional
properties.

Key words: nut,
nutrition, tuber, health, benefit

INTRODUCTION

Tiger nut (Cyperus esculentus var. sativus),
an emergent grass- like plantbelonging to the sedge family, is also found to be a
cosmopolitan perennial crop of the same genus as the papyrus plant that
is common in seasonally flooded wetlands [1, 2]. It
is widely distributed in the temperature zones within South Europe as its
probable origin, and has become naturalized in Ghana, Nigeria and Sierra Leone [3]. Tiger nut is one of the earliest domesticated crops and in fact, was
found in vases and was used to embalm bodies of the Egyptian Pharaohs [4]. In Nigeria, tiger nut is available in fresh, semi-dried and dried form in the markets where it
is sold locally and consumed even uncooked. Tiger nuts are under-utilized due
to lack of information on their nutritional potential [5]. A
lot of people eat the tiger nut without knowing the nutritional benefits and
products that can be obtained from it like tiger nut oil and milk. The
purpose of this review was to bring together some of the data on the uses,
health and economic benefits of the tuber of the tiger nut that is completely unexploited in Nigeria.

Tiger nut as a plant

Tiger
nut is a tough erect fibrous-rooted perennial plant, 1 to 3 ft high,
reproducing by seeds and by many deep, slender rhizomes, which form weak
runners above the ground, and small tubers or nutlets at the tips of
underground stems [6]. This native perennial sedge is ½2 inches tall
and unbranched. The central stem is erect, 3-angled, and mostly covered by the
sheaths of the leaves. The leaves tend to congregate toward the base of the
plant. The leaf blades are up to 1½ inches long and 1/3 inches across; they are
light green and glabrous, spreading outward from the stem. There is a
conspicuous channel along the central vein of each leaf blade, especially the
larger ones. The leaf sheaths are whitish green, closed, and hairless;
sometimes they become pale red towards the base of the plant [7]. The central
stem terminates in an umbel or compound umbel of floral spikes; the size and
shape of the umbel is rather variable (on larger plants, it is usually several
inches across). Each umbel has 1-3 sessile spikes and 6-10 non-sessile spikes
on straight branches of varying length. At the base of each umbel or compound
umbel of spikelets, there are several leafy bracts of varying length; the
largest bract is usually longer than the inflorescence. Each floral spike is
about 2-3 inches long, consisting of 4 ranks of spikelets along its central
stalk (or rachis). The central stalk is flattened and narrowly winged. The
spikelets are perpendicular to this stalk and about ½¾ inches long. The
spikelets are yellow to golden brown, narrowly linear, and flattened in shape;
they consist of 10-30 florets and their scales. The overlapping scales are slightly
spreading along the length of each spikelet; each scale is 2.03.0 mm. in
length. Each floret has a white tripartite style and yellowish brown anthers;
the tips of the styles are curly. The blooming period occurs from mid-summer to
early fall.

Pollination of the tiger nut
plant is by wind [8]. The florets are replaced by small achenes that are
1.01.5 mm. long, oblongoid or oblongoid-obovoid, and flattened. The shallow
root system is fibrous, rhizomatous, and tuberous. The white rhizomes have a
slightly segmented appearance from the brown margins of their outer membranes;
the rhizomes are connected to small globoid tubers up to ½ inch across. Young
tubers are white, while older tubers are covered by a yellow outer membrane; they
are usually found within 6 inches of the ground surface. Vegetative colonies of
plants are often produced from the tubers and their rhizomes. The nutlets are almost smooth at maturity and unevenly
globe shaped [8]. High temperatures and low
nitrogen levels increase tuber production and an increased day length (by
lighting) will reduce tuber formation. The tuber epidermis (skin) contains
substances, which inhibit sprouting of tubers; the plant grows best in moist sandy-loam soils but will grow in the hardest clay, tolerates high soil moisture and is intolerant to shade
[8, 9]. The plant produces small, oblong
tubers in abundance, which are sweet and rich in fat [10].

It has many other names like Zulu nut, yellow nutgrass,
ground almond, chufa, edible rush and rush nut [11]. In Nigeria, the Hausas call it Aya, Yorubas imumu, the igbos
ofio, aki Hausa in southern Nigeria [12]. Tiger nuts which are
incorrectly called nuts or nutlets, thus the origin of their common name, are small about the size of a peanut
growing at the rhizome of the plant [13]. Like other sedges, the plant is
most frequently found inhabiting wet marshes and edges of streams and ponds
where it grows in coarse tufts [14]. Tiger nut tubers are daily ingredients of
the diet of many people in North Africa and Spain [15]. In North Africa, the
tubers are consumed in their natural form or after being soaked in water for
some hours. In Spain, the tubers are consumed mainly as a drink called locally horchata
de chufa (chufa milk). This plant was originally native to the Mediterranean
region but its cultivation has now spread to many warm countries [16]. It is
usually sown in April and picked in November [17]. There are mainly three varieties namely: black, brown and yellow, and only yellow and brown are readily
available in the Nigerian markets. The yellow variety is preferred to all other
varieties because of its inherent properties like its bigger size, attractive
colour and fleshier body. The yellow variety also yields more milk,
contains lower fat and higher protein and less anti-nutritional factors
especially polyphenols [18].

In Northern Nigeria, the nut can be bought in the market all year round. The weight of fresh
tuber ranges from 70mg to about 900mg while the weight of dried tuber ranges
from 30mg to 350mg. A dried tuber nut can absorb up to three times its own
weight of water. A single tuber can produce nearly 2000 plants and 7000 tubers
in one growing season. It was observed that tiger nut production is
predominantly the work of women farmers as high as 70% and 30% men [13]. The
nuts are valued for their highly nutritious starch content, dietary fibre,
digestible carbohydrate (mono, di and polysaccharides) [14, 19]. The nut was
reported to be rich in sucrose (17.4 to 20.0%) and fat (25.50%) which are
resistant to peroxidation, and protein (7-8%) [9, 20, 21] as indicated in Table
1. The nut is also fairly rich in mineral content (Sodium, Calcium, Potassium
Magnesium, Zinc and traces of Copper) [22]. Tiger nut has been cultivated as a
livestock food and for human consumption; it can be eaten raw, roasted, grated,
baked or used for ice cream and beverage making for its many useful benefits
[22, 23]. They taste best when dried. They are generally dried out (mostly in
the sun), a process that takes one or more months with occasional turning over to
ensure uniform drying to preserve them and to eliminate prevailing rot or any
microbial infection. This secures their nutritional quality although,
unfortunately, as they dry, they become wrinkled. As they dry, temperature and
relative humidity are monitored. Once dry, they can be kept for several years,
to be reconstituted by soaking overnight or by boiling when ready to serve them
[23]. The nutritional value of tiger nut derivatives, like oil and milk, arises
from the very composition of the tiger nut. The level of anti-nutrients such as
tannins, alkaloids and polyphenols is drastically reduced by soaking in water
for 6 hours, thereby making it free of unwanted elements especially in making
the milk [24].

Tiger nut milk

The
origin of the use of this tuber for making milk is exclusive to the Spaniards to
which it may have been introduced by the Arabs. Tiger nut milk/beverage/drink
commonly called kunnu aya in northern Nigeria is a healthy drink with
many nutrients. It is a nourishing and energetic product recommended by experts
to be taken during any season of the year, especially in dry season when the
sun is hot. In Spain, it is called chufa de horchata. It is a rich
source of nutrients such as vitamins C and E, and minerals such as phosphorus,
magnesium, potassium, calcium, iron, and also carbohydrates, unsaturated fats,
proteins and some enzymes which help in digestion [25]. In fact this drink
contains more iron, magnesium and carbohydrates than the cows milk [26]. It
has also the advantage of not containing lactose, casein, sugar or proteins of
the milk, or cholesterol and is therefore an ideal drink for people who do not
tolerate gluten or cows milk [23]. The nutritional value of tiger nut beverage
is, however, insufficient given that its protein content is low (6.05%) [25, 27].
The production process for tiger nut milk is shown in Figure 1.

Tiger
nut flour

Tiger nut
flour has a unique sweet taste, which is ideal for different uses. It is a good
alternative to many other flours like wheat flour, as it is gluten free and
good for people who cannot take gluten in their diets. It is also used in the confectionery
industry [23, 28]. It is considered good flour or additive for the bakery
industry, as its natural sugar content is fairly high, avoiding the necessity
of adding too much extra sugar [29]. Also, it can be used as a flavoring agent
for ice cream and biscuits [30]. In the Keta area of Ghana, the sun-dried
tubers are ground to a fine powder to which sugar can be added to be stored
till required. Roasted tubers may be similarly ground to a powder known in Vhe
(Awlan) as fie-dzowe. These meals may be eaten alone or with water added to
make a beverage [31]. In addition, tiger nut has been demonstrated to contain
higher essential amino acids than those proposed in the protein standard by the
FAO/WHO [28] for satisfying adult needs. Therefore, tiger nut, with its
inherent nutritional and therapeutic advantage, could serve as good alternative
to cassava in the baking industry [32].

Furthermore, tiger
nut flour does not lose any of its nutritious properties in the milling
process. The fine ground tiger nut flour gives baits a smooth, creamy texture
with a distinctive taste fish love, and can be incorporated into any mix as
base ingredient, allowing baits to retain moisture [33]. Incidentally, cutting
part or all of the skins off tiger nut hook baits makes them more effective.
Part of tiger nuts attraction is that they are rich in lysine, a major fish
feeding stimulant though tiger nuts also contain many other extremely important
and stimulatory dietary essential amino acids for fish, including methionine,
cystine, arginine and histidine [34, 35]. The production process for tiger nut
flour is shown in Figure 2.

Tiger
nut oil

The edible and stable oil obtained
from the tuber is said to be superior oil that compares favourably with olive
oil. The oil is golden brown in colour
and has a rich, nutty taste [17]. The oil remains in a uniform liquid form at
refrigeration temperature. This makes the oil suitable for salad making. It has
a high oleic acid and low polyunsaturated fatty acid (linoleic acid and linolenic
acid) [36, 37], enough to cover daily minimum needs for an adult (around 10 g)
and low acidity, and so is excellent for the skin. It also has higher oxidative
stability than other oils, due to the presence of polyunsaturated fatty acids
and gamma-tocoferol [37]. It is regarded as high quality oil due to its
extraction without adding any external heat (cold pressed oil), and is highly
recommended for cooking over other oils because it is more resistant to
chemical decomposition at high temperatures [38]. Furthermore, less fat is
absorbed into the food as it creates a crust on the surface during cooking,
preventing the oil itself being absorbed into the product. In the textile
industry, the oil is used to waterproof textile fibres. The oil compares well
with corn, soybean, olive and cotton seed oil and can thus serve as a
substitute for these oils especially in times of scarcity [39]. The oil is a
potential source of biodiesel and much research has been conducted [40]. The
production process for tiger nut oil is shown in Figure 3.

According to Mason [13], tiger nuts have long been
recognized for their health benefits as they have a high content of soluble
glucose and oleic acid, along with high energy content (starch, fats, sugars
and proteins), they are rich in minerals such as phosphorous and potassium, calcium,
magnesium and iron necessary for bones, tissue repair, muscles, the blood
stream and for body growth and development and rich in vitamins E
and C. Sugar-free tiger nut milk is suitable for diabetic people and also helps
in weight control [41], due to its content of carbohydrates with a base of
sucrose and starch (without glucose), and its high content of Arginine, which
liberates the hormone that produces insulin [25,42]. It is recommended for
those who suffer from indigestion, flatulence and diarrhoea because it provides
digestive enzymes like the catalase, lipase and amylase. The high content of
oleic acid has positive effect on cholesterol, thereby preventing heart
attacks, thrombosis and activates blood content of soluble glucose. Tiger nut
reduces the risk of colon cancer. It prevents constipation. Tiger
nut contains a good quantity of vitamin B1, which assists in balancing the
central nervous system and helps to encourage the body to adapt to stress [25,
43]. The
milk supplies the body with enough quantity of Vitamin E, essential for
fertility in both men and women. Vitamin E also delays cell
aging, improves elasticity of skin and helps to clear the appearance of
wrinkles, acne and other skin alterations.

In China, tiger nut milk is used as a liver tonic, heart
stimulant, drank to heal serious stomach pain, to promote normal menstruation,
to heal mouth and gum ulcers, used in Ayurvedic medicines and is a powerful
aphrodisiac (sexual stimulant).The
black species of the tiger nut is an excellent medicine for breast lumps and
cancer. The tubers have a relatively high total
antioxidant capacity, because they contain considerable amounts of
water-soluble flavonoid glycosides. Consumption of antioxidants could protect
the immune system of malnourished populations. The intake of antioxidant-containing
foods may delay the progression of HIV infection to AIDS [44].

For many years,
the tiger nut tubers have been considered to have adequate properties to fight
respiratory infections, and some stomach illnesses. To this date, the Horchata
de chufa is considered an effective remedy for diarrhea, according to
popular tradition in Valencia, Spain. It promotes the
production of urine and this is why it is a preventive measure for cyst,
prostrate, hernia, rectum deformation and prolapsed (anal feature-small painful
flesh at the tip of the anus) and to prevent endometriosis or fibrosis as well
as blockage of the tip of the fallopian tube. The oil reduces low density lipoprotein-cholesterol (LDL-C)
and increases high density lipoprotein-cholesterol (HDL-C) [23], reduces levels
of triglycerides in blood and the risk of forming bloody clots, thereby preventing
arteriosclerosis. It also stimulates the absorption of calcium in bones and the
production of new bony material, due to short and medium chain fatty acids,
oleic acid and essential fatty acids [14]. It is also recommended for infants
and the elderly because of its high content in Vitamin E and its antioxidant benefits
in the cell membrane [43].

In the United States, the primary use of tiger nut as a
crop is to attract and feed game, particularly wild turkeys. Turkeys love tiger nut tubers; as natural scratchers, once discovering a plot of chufa, they will
return again and again, all winter long, or until spring arrives and other food
is readily available [25]. Tiger nut tubers have been planted so that pigs
could be attracted to the fields to fatten and improve the taste of pork. The
tubers have been used as hog feed, pastured in the field in states such as Florida, Georgia, and Alabama. Tubers of tiger nut have also been identified as valuable
food for waterfowl and cranes. Ducks dive for them when wetland fields are
flooded. It is also used in seed mixes for wetland restoration, mitigation, and
erosion control. The caramel from malted tubers of Cyperus esculentus
may be used to add body, flavor, or color to certain baked products,
non-alcoholic malt beverages and dark beers, and in the production of
condiments. The starches obtained from tiger nut and rice showed similar
properties; the solutions of the starch exhibited a good paste stability,
clarity, and adhesive strength. The starch can be used in many starch-based
foods as well as in the cosmetic industry, and for laundry, glazing and
stiffening. The waste residue after oil extraction could be further modified to
produce syrups, flours, or livestock feeds [27, 44].

CONCLUSION

Although tiger nut is largely unexploited, cheap and eaten
without much knowledge of its benefits, there is an urgent need for awareness
campaigns on its health and nutritional benefits.